Word processing systems have evolved from relatively simple text processors which facilitated the manipulation of character strings to the sophisticated multitasking processors of today which are capable of such diverse applications as communications, calculations and data processing emulations. It is not uncommon, for example, to provide a word processing system with a calculation application to include the generation of graphics data based on calculated or input numerical data. This is because it is often easier to interpret the numerical data when it is presented as a bar, pie or line graph, for example.
The problem arises, however, in the presentation of the graphics data. Generally, the visual display of graphics data on a CRT display has been accomplished with an All Points Addressable (APA) display. Word processing systems typically use a character box or non-APA display. The advantage of the character box display is that it requires much less memory than an APA display of even moderate resolution. The disadvantage in so far as the presentation of graphics data is concerned is the inability of the character box display to support the display of characters not defined by the character box.
Printing the graphics data is another problem because most business level word processing systems employ letter quality printers of the type wherein a fully formed character is imprinted on the paper by a single stroke. Typical of such letter quality printers are printwheel printers. The printwheels on these printers usually have 96 petals, each having a single character. In the past, printing of graphics data has usually been accomplished with a dot matrix printer or a plotter. While the dot matrix printer and the plotter do an excellent job of printing graphics data, neither is an acceptable substitute for the printing of alphanumeric characters. The user of a word processing system has therefore been faced with the requirement of purchasing two printers in order to obtain quality printing of both alphanumeric characters and graphics data. However, the logistics of using two different printers, expecially when the same page is to be imprinted by both, is not at all satisfactory.
The above referenced U.S. Pat. No. 4,555,700 entitled "Internal Image and Bit Array for Diplay and Printing of Graphics" discloses an apparatus which provides a word processing system using a non-APA display and a letter quality printer, both character box devices, with the ability to both display and print graphics data. The invention described in that application provides an internal image and bit array apparatus to contain the data structures necessary and sufficient to both display and print the graphics data. These data structures are (1) output by the process that converts numeric data values into image data and (2) input to the display process and the print process. These are the central mechanisms that makes graphics on a character box device possible.
A problem arises, however, when the operator of the word processing system desires to correct or annotate the displayed image. For example, in a typical application, the operator first enters numeric data and then presses the appropriate key to request that the numeric data be converted into a bar, pie or line chart. As a result, an image of the chart is calculated and displayed to the operator. In many cases the operator would want to annotate the displayed image with titles, notes or other alphanumeric data. Such data would normally be written into internal image and if conflicts arise as a result of superimposition of displayed data, the annotation characters added by the operator are written over the previous data. As a result, if the operator changes his mind and deletes some of the added annotation data, the previous data which was written over is lost and can not be redisplayed.